Reconstructing the anatomy of prehistoric sharks isn’t easy. With few exceptions – an exquisitely-preserved body fossil here, some calcified bits of skeleton there – teeth make up the majority of the shark fossil record. When those teeth come from a relatively recent species with close living relatives, it is not difficult to imagine what the extinct species might have looked like. The further back in time you go, though, the more bizarre sharks become. Sometimes teeth are not enough, and one especially unusual set of teeth has vexed paleontologists for over a century.

At first sight, the teeth didn’t look like they belonged to a shark at all. Coiled upon itself in a circular whorl, the bizarre tooth row superficially resembled